I don’t know exactly what your question is, but perhaps have a look at [url=http://www.fmod.org/docs/HTML/FSOUND_Stream_SetEndCallback.html#:3vr88umy]FSOUND_Stream_SetEndCallback()[/url:3vr88umy] ?

And the FMUSIC_IsPlaying() requests a pointer on a mod, not channel.
Only the FSOUND_IsPlaying() requests a pointer on a channel, but when you start playback you have to specify a channel, and so you know it ?!